When I couldn’t figure out how ice becomes suspended above the water level, except for the obvious reason, I reached out to two physicists for enlightenment. One wrote back. Below is my question, and an answer from Dr. Chris Baird, who runs a website called Science Questions with Surprising Answers (sciencequestionswithsurprisinganswers.org). Turns out I should not have rejected the obvious reason (story of my life).

Hello, Chris Baird,

Last week I took several photographs around the edges of a nearby pond where ice had formed on twigs and trailing branches a few inches above the water. At first I thought that the ice had formed while the water level was higher, but somehow I don’t think that explains it. Then I wondered if light snow flakes fell on these sticks and branches and didn’t make it all the way to the water. Then they somehow transformed themselves from snow to ice. (Probably also a wrong answer.) Do you know how this happens?

Linda Grashoff

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Hello Linda,

While it’s hard to know for sure from 2D photos, I believe that your first notion is correct. The ice formed on the surface of the water while the water was at a higher level. The ice froze around the stems and became anchored to the stems. As the water level gradually dropped, ice patches away from the stems lowered with the water, staying in contact with the water, and thus melted away when the water warmed up. In contrast, the ice anchored to the stems stayed put when the water level lowered. They therefore lost contact with the water and did not melt when the water warmed up. This explanation is suggested by the disc shapes of the ice and the fact that these discs sit at levels that are good anchor points (i.e. the tips of stems, the junction points of stems, and the points in stems that have a crooked shape). These shapes are complex enough that there may have a been a complex series of events involving partial melting, refreezing, and repeated rising and lowering of the water level.

Snowfall is crystalline in nature and does not form solid chunks of transparent ice on stems. Freezing rain can form ice masses on stems, but it does not form disc shapes at only a few locations. Rather, freezing rains forms a thin layer of ice that coats the entire stem.